A. Technical Field
The present invention relates to inductive switching converters and, more particularly, to systems, devices, and methods of utilizing zero-current and zero-voltage switching to reduce transition losses in DC/DC converters.
B. Background of the Invention
The electronics industry has continually demanded higher switching regulator efficiencies. Switching regulators transfer energy from a given input voltage level to a higher or lower output voltage level for delivery to a load. Inductive switching converters take advantage of in important physical property of inductors, the resistance to any changes to the current the inductor carries, in order to transform an input voltage to a desired output voltage. The level of the output voltage is adjusted by controlling the operation of active switching elements within the switching regulator.
Typical efficiencies of DC/DC converters have reached about 96%, such that a reduction of power losses by an additional one or two percent can reduce existing power losses by as much as 50%. Aside from conduction losses in the turned on active devices, which are typically transistor power switches, one major source of power dissipation in switching regulators are transition losses. There are two types of transition losses that occur during the switching process, the first type is capacitive loss resulting from charging and discharging a parasitic capacitance at the switching node of the converter. The second type of transition loss is conduction loss associated with turning on a power switch having a large voltage and non-zero inductor current present at the same time. This second type of transition loss is exacerbated by reverse recovery current in the power switch due to the body diode in the switch being forward biased.
Some existing approaches reduce switching power losses by avoiding transitions from a low voltage to a high voltage by applying zero voltage switching (ZVS) or zero current switching (ZCS) methods. In order to perform ZVS, by definition, the voltage across a switch needs to be at a near zero value at the time the switch is being turned on. However, existing ZVS or ZCS topologies have major drawbacks. For example, ZVS or ZCS buck converter topologies require (lossy) discontinuous current mode operation with average inductor current values that have to be approximately two times larger than the output current, as the inductor needs to reach zero for the switching regulator to actually perform ZVS or ZCS. A 10 A output current, for example, typically requires a 20 A peak current. Existing ZVS or ZCS topologies, by definition, require an inductor current that approaches zero, thus, conduction losses are typically more than twice as high as in continuous current buck converters that have very low ripple content. Alternative approaches address this problem by either employing resonant or critical conduction topologies. However, these approaches create more problems than they solve and do not result in higher system efficiency at higher ripple currents due to increased conduction losses associated with resonant or critical conduction topologies. What is needed are tools for switching regulator designers to overcome the above-described limitations.